The invention relates to battery-power control and, more particularly, to low battery indicators.
Battery-operated devices, such as notebook computers and personal digital assistants, for example, typically monitor some indication of remaining battery capacity in order to ensure that enough capacity remains to perform critical operations. For example, a battery-operated computer may need to perform an orderly shutdown, which may include relatively power-hungry operations such as a xe2x80x9csave-to-diskxe2x80x9d, before the available battery capacity is depleted.
Battery voltage may be used to develop a warning signal that indicates that battery capacity has reached a level that only allows for the safe execution of one last critical task, such as a computer shutdown operation.
However, voltage alone provides an inadequate measure of remaining useful battery capacity (i.e., remaining energy available at a useful voltage, typically stated in milliamp-hours). For example, battery discharge rates can affect a battery""s apparent remaining useful capacity. At a low discharge rate D1, the battery""s voltage may indicate that a capacity Q1 remains, the voltage at a moderate discharge rate D2 may indicate that a different capacity Q2 remains, and the voltage at a high discharge rate D3 may indicate that a third capacity Q3 remains. If a battery-operated device""s critical operation requires, for example, a capacity Q2 at discharge rate D2, a voltage measurement at a discharge rate of D1 may indicate that the battery""s remaining capacity meets or exceeds the critical capacity/discharge rate Q2/D2 requirement, when, in fact, it doesn""t. Similarly, given a critical capacity/discharge rate Q2/D2, a voltage measurement at a higher discharge rate D3 may indicate that the critical capacity/rate Q2/D2 has been reached before, indeed, it has.
Due to the effect that different discharge rates have on a battery""s useful energy capacity, battery-operated system designers typically xe2x80x9cover-engineerxe2x80x9d the system to ensure that there is sufficient remaining useful battery capacity to allow a critical operation, such as a shut-down operation, to be performed before the useful battery capacity is xe2x80x9cexhausted.xe2x80x9d This sort of xe2x80x9cworst-casexe2x80x9d design effectively limits the useful capacity of a system to that associated with worst-case battery drain.
A system and method for monitoring and reporting battery capacity that permits the full usage of a battery""s capacity would therefore be highly desirable.
In a battery monitoring system and method in accordance with the principles of the present invention, a capacity of interest is determined. This capacity of interest is the useful battery capacity required for an operation of interest; that is, the battery capacity at the discharge rate required for the operation of interest. The operation of interest may be a save-to-disk operation during a battery operated computer shutdown, a shutdown procedure for a personal digital assistant, or the sounding of a low-battery alarm for a cellular telephone, for example. Given the capacity of interest, alarm settings (also referred to herein as indices or flags) are determined for a variety of voltage and discharge conditions. The indices map voltage and discharge rate information for one or more discharge rates to the capacity of interest.
When an indexed battery-voltage/discharge-rate combination that corresponds to the capacity of interest is encountered, an alarm may be activated to indicate that, although the present voltage and discharge rates may indicate that there is more or less capacity than required for the operation of interest, the capacity of interest (useful energy left at the discharge rate of interest) has been reached.
A battery monitoring system and method in accordance with the principles of the present invention may also include a temperature sensor that permits the trip points to be adjusted for variations in the temperature of a battery being monitored. The monitoring system will be particularly useful in battery charging systems, battery-powered electronic devices, such as computers (laptop, notebook, handheld, etc.), personal digital assistants, pagers, and cellular telephones, for example.